Many different systems and methods, depending on application, are available for dissolving gases in liquids. Some of the main applications are the oxygenation of outdoor water bodies, industrial uses, and the treatment of wastewater. Most dissolved gas delivery methods (i.e. bubble diffusion, Venturi injection, U-tubes, Speece cones) are based on increasing the contact time and/or surface area of gas bubbles introduced into a bulk liquid to enhance mass transfer. Previous technologies for dissolving gas into a liquid have features that increase the contact time and/or contact area between gas bubbles and bulk fluid to increase dissolution. Most, if not all, of these earlier technologies require recovery systems for off-gases that do not dissolve into the fluid or allow loss of undissolved gases.
U.S. Pat. No. 5,979,363 (issued to Shaar) describes an aquaculture system that involves piping a food and oxygen slurry into a pond. U.S. Pat. No. 5,911,870 (issued to Hough) proposes a device for increasing the quantity of dissolved oxygen in water and employs an electrolytic cell to generate the oxygen. U.S. Pat. No. 5,904,851 (issued to Taylor et al.) proposes a method for enriching water with oxygen that employs a Venturi-type injector to aspirate gas into a fluid, followed by mixing to increase dissolution. U.S. Pat. No. 5,885,467 (issued to Zelenak et al.) proposes mixing a liquid with oxygen using a plurality of plates or trays over which the liquid flows gradually downward. U.S. Pat. No. 4,501,664 (issued to Heil et al.) proposes a device for treating organic wastewater with dissolved oxygen that employs several process compartments. U.S. Pat. No. 5,766,484 (issued to Petit et al.) proposes a dissolved gas flotation system for treatment of wastewater wherein the relative location of inlet and outlet structures reportedly maximizes the effect of air bubbles in separating solids from the fluid. U.S. Pat. No. 5,647,977 (issued to Arnaud) proposes a system for treating wastewater that includes aeration, mixing/flocculating, and contact media for removing suspended solids, etc. U.S. Pat. No. 5,382,358 (issued to Yeh) proposes an apparatus for separation of suspended matter in a liquid by dissolved air flotation (DAF). U.S. Pat. No. 3,932,282 (issued to Ettelt) proposes a dissolved air flotation system that includes a vertical flotation column designed with an aim of preventing bubble breakage.
Mazzei injectors (see, e.g., U.S. Pat. Nos. 5,674,312; 6,193,893; 6,730,214) use a rapid flow of water to draw gas into the fluid stream; mixing chambers may or may not be used to increase contact time between the gas bubbles and the fluid to increase dissolution. The method of Keirn (U.S. Pat. No. 6,530,895) has a series of chambers under pressure that add gaseous oxygen to fluid; the pressure increase and the chambers in series are used to increase dissolution. U.S. Pat. No. 6,962,654 (issued to Arnaud) uses a radially grooved ring to break a stream of fluid into smaller streams; gas is introduced into the streams and mixing is used to increase dissolution. Speece (see U.S. Pat. Nos. 3,643,403; 6,474,627; 6,485,003; 6,848,258) proposes use of head pressure to introduce liquid under pressure into a conical chamber; the downward flow of the fluid is matched in velocity to the upward flow of gas bubbles to increase dissolution time. Littman et al. (U.S. Pat. No. 6,279,882) uses similar technology to Speece except that the upward flowing bubble size is decreased with a shockwave. Roberts, Jr. et al. (U.S. Pat. No. 4,317,731) propose turbulent mixing in an upper chamber to mix gas with a bulk fluid; a quiescent lower chamber allows undissolved gas to rise back into the upper chamber for remixing. The following U.S. patents use various methods to increase the contact time between gas bubbles in fluids: U.S. Pat. No. 5,275,742 (Satchell Jr. et al.); U.S. Pat. No. 5,451,349 (Kingsley); U.S. Pat. No. 5,865,995 (Nelson); U.S. Pat. No. 6,076,808 (Porter); U.S. Pat. No. 6,090,294 (Teran et al.); U.S. Pat. No. 6,503,403 (Green et al.); U.S. Pat. No. 6,840,983 (McNulty).
An object of the present invention is to provide a simplified, low cost method and apparatus for rapidly increasing the dissolved gas levels in a liquid. A further object of the present invention is to introduce a spray of fluid into a gaseous headspace under pressure in order to greatly increase the rate and degree of dissolution and, if needed, use the pressure within the system to provide energy for mixing.